In conventional drill stem testing a packer and a normally-closed test valve are lowered into the well bore on a pipe string, and the packer is set to isolate a formation interval to be tested. The test valve is opened and then closed for respective flow and shut-in periods of time, during which changes in fluid pressure in the well bore below the valve are recorded by a gauge. The pressure data normally is not available for inspection or analysis until the test tool string including the gauge is withdrawn from the well.
Drill stem testing systems have been proposed that enable a concurrent surface indication of conditions measured downhole while the test is underway. Examples of such systems are shown in U.S. Pat. Nos. 2,607,220 and 3,041,875. A surface readout is, of course, desirable from the standpoint of being able to determine whether the durations of the flow and shut-in periods have been sufficient, as well as providing immediate detection of tool plugging or other malfunction. However, in accordance with the disclosure of the above-mentioned patents, and as employed in certain drill stem testing systems in current use, the electrical connection through which signals are fed to the surface via cable is mounted on the test tool in alignment with the center of the tubing bore. This fact, together with the type valve employed, blocks vertical access through the tool string so that it is not possible to run a wireline tool such as a perforating gun therethrough. This capability requires the use of a so-called "full-bore" test tool that includes a ball or flapper type valve which provides for straight vertical access through the tool when moved to the open position. Although full-bore test tools are known, none of the prior structures that applicants are aware of have any provision that enables surface readout of downhole measurements while the testing is in progress.
It is accordingly the general object of the present invention to provide a new and improved full bore drill stem testing apparatus including means enabling a concurrent surface readout of measurements made downhole while the test is in progress.